In general chopper drums are provided with blade holders which together with their blades are uniformly spaced about the circumference of the drum body in a plurality of annular rows. The blade holders are detachably connected to the drum body so that the chopped-stalk length can be modified and the number of blades arranged on the drum body can be varied.
German patent No. 955 370 describes a chopper which is provided with curved worm-like blades subdivided into segments in which these blades are counter-coiled, i.e. curved in opposite senses. The bent worm-like sections extend inward beyond the center of the drum. In addition, such choppers have vanes at both outer ends of the drum body to generate additional flow streams via respective air channels.
Such curved worm-like chopping blades as well as those with chopping blades extending obliquely to the center of the drum have the disadvantage of poor discharge of the chopped material in the center area of the drum thus causing congestions or packing of the cut material. The chopped-stalk material is thrown by the obliquely extending blades and impellers against the adjacent chopping blades and respective blade holders by which it is expelled forward out of the chopper drum. Consequently, energy losses as well as losses of crop material are suffered.
German utility model No. 76 09 165 describes a field chopper including a drum which supports continuous blades or beating bars. By providing a shovel-type formation, the chopper generates a hurling of the crop material. Associated with each second blade is an impeller which is arranged symmetrically to the blade drum and is keyed to it or fastened to the drum by wedges. According to this disclosure, the blades are provided with a lagging cutting shape and the impellers are inclined so that the crop material after being cut and supplied to the impellers is thrown off easier and in an optimum manner.
This arrangement has the disadvantage that the crop material is pushed against the sides of the drum housing especially when cutting at a sharp blade pitch. Consequently, friction is obtained resulting in energy losses. The friction along the side walls also causes a penetration of chopped material into the interior of the drum. Although the crop material will partly be carried away by the impeller, those portions of the chopped material disposed in the central zone of the drum cannot be transported off anymore.